I had brain fog on Miracle-Mineral-Supplement as well, intermittently and especially after getting up around 15 drops 2x/day. Like you, I also thought I might have to quit Miracle-Mineral-Supplement , because my job requires that I be able to use my brain and I couldn't continue trying to make it through each day like a half-zombie. Luckily, however, the brain fog lifted (as in, pre-MMS levels) on its own after a couple of weeks while I still continued with the Miracle-Mineral-Supplement . But then again, I don't have Lyme (or at least I'm not aware of it). So I would suggest to see if you can push through it.
I should add though that the only real improvement I saw with brain fog was after my first (and only) liver flush, which I did after using MMS. In my layman's opinion, I think that using MMS results in your liver becoming heavily weighed down with toxins caused by the MMS-induced die off. Thus, by flushing it out you are helping the process toward finally getting the pathogens and their dead cells/toxins out of you. And there is definitely some sort of connection between a toxin-heavy liver and brain fog.